Smart material actuators heretofore have used the expansion/contraction characteristics of a smart material to effect movement of an output member. Smart materials include but are not limited to piezoelectric materials, magnetostrictive materials, electroactive polymers, electrostrictive materials, shape memory alloys, and smart hydrogels. Piezoelectric stacks have often been used as the primary mover in such actuators.
Smart materials typically demonstrate a low percentage of nominal length increase at their maximum excitation. This often presents a need for stroke amplification for many applications including, inter alia, valves for liquid or air flow control, pin actuators for printer heads, control surface actuators for aerospace applications, high-power-density hydraulic pumps, etc.
Several known piezoelectric or electroexpansive actuator devices have been connected with levers and side linkages to produce motion amplification. In those cases, a high force, short stroke expansion or contraction of a piezoelectric actuator is amplified as a lower force, longer stroke movement.
In U.S. Pat. No. 4,318,023, a saggitally amplified mechanism is described in which a lever arm is pivotally connected to a fixed base support and is driven for movement by an electroexpansive actuator. The end of the lever arm, opposite the pivot end, is connected to one end of a saggital tension member. The opposite end of the saggital tension member is connected to the fixed base support. Upon actuation of the electroexpansive actuator, the lever arm is pivoted to increase the tension on the saggital member and cause the midpoint of the saggital member to be moved in a direction perpendicular to the longitudinal axis defined between the end points of the sagittal tension member. U.S. Pat. No. 4,769,569 shows a piezoelectric stack motor stroke amplifier in which a rigid frame supports a pair of stack motors. The stack motors act in opposition against a movable output actuator to provide an amplified push stroke output actuation.